The ap program treats each argument as one or more addresses, and prints those addresses out in the official RFC 822 format. Hence, it is usually best to enclose each argument in quotes for the shell.

To override the output format used by ap, the -format string or -format file switches are used. This permits individual fields of the address to be extracted with ease. The string is simply a format string, and the file is simply a format file. See mh-format(5) for the details.

In addition to the standard escapes, ap also recognizes the following additional escape:

Escape Returns  Description
error   string   A diagnostic if the parse failed

Here is the default format string used by ap:

%<{error}%{error}: %{text}%|%(putstr(proper{text}))%>

which says that if an error was detected, print the error, a `:', and the address in error. Otherwise, output the RFC 822-proper format of the address.